Process for oxidizing olefins to aldehydes and ketones



' favor the complex formation.

United States Patent 3,301,905 PROCESS FOR OXIDIZING OLEFINS T0 ALDEHYDES AND KETONES Wilhelm Riemenschneider, Kurt Dialer, and Otto Probst, Frankfurt am Main, and Otto-Erich Bander, Hoflreim, Taunus, Germany, assignors to Farbwerke Hoechst Aktiengesellschaft vormals Meister Lucius & Bruning, Frankfurt am Main, Germany, a corporation of Germany Filed Jan. 26, 1961, Ser. No. 84,968 Claims priority, application Germany, Sept. 28, 1957, F 24,051; Sept. 26, 1957, F 24,034 6 Claims. (Cl. 260-597) The present invention relates to a process for oxidizing olefins to aldehydes, ketones and acids. This application is a continuation-in-part of application Ser. No. 673,691, filed September 26, 1958, now abandoned.

It has already been proposed to oxidize ethylene catalytically by means of an argentiferous catalyst to ethylene oxide, or by means of an oxidation catalyst other than a silver-containing catalyst at a raised temperature to obtain mixtures of formaldehyde, acetaldehyde, formic acid, acetic acid and other products. These processes, however, do not produce acetaldehyde or acetic acid in a yield interesting from an economical point of view. Own experiments have revealed that the oxidation carried out under such conditions in the presence of a noble metal catalyst likewise involves small yields of acetaldehyde, and the relative proportion of formaldehyde obtained generally preponderates.

It is also known that compounds of palladium, platinum, silver or copper form complex compounds with ethylene. Furthermore, the formation of acetaldehyde was observed in decomposing a potassium-platinum-complex compound. Other unsaturated compounds may In this case stoichiometric reactions are concerned yielding the noble metal as such.

It has also been described to reduce palladous chloride by means of ethylene in the presence of water to palladium metal. In this reduction the formation of acetaldehyde was observed.

Still further, it has been described that palladous chloride dissolved in Water can be reduced rapidly and completely to palladium by means of propylene, even it propylene is admixed with nitrogen or air. It has also been described to reduce palladous chloride by means of isobutylene under the same conditions. It is, however, known that carbon dioxide is not evolved either in this latter reduction or in those reductions which are carried out in the presence of ethylene or propylene as a reducing agent.

In application Ser. No. 747,116 filed July 8, 1958 and now Patent No. 3,154,586 in which two of the present inventors are co-inventors, a process is described according to which carbonyl compounds can be obtained from the corresponding olefins in a good yield and, if desired, in a continuous manner by contacting said olefins with an oxidizing agent, a liquid catalyst having an acid to neutral reaction and comprising water, a compound of the noble metals belonging to group VIII of the periodic table and a redox system.

It is furthermore described in application Ser. No. 750,150, filed July 22, 1958 and now Patent No. 3,122,586 in which one of the present inventors is a co-inventor, to contact the olefin and the oxidizing agent separately with the liquid catalyst. According to said application the reaction may be performed by contacting the liquid catalyst with the olefin and the oxidizing agent in several reaction vessels. Instead of pure olefin a mixture of oxygen and olefin may be used in which the oxygen content is outside the range of explosivity, i.e. for example be- Patented Jan. 31, 1967 tween 1 and 10%, calculated upon the amount of olefin used.

In application Ser. No. 747,115, filed July 8, 1958 and now abandoned in which likewise two of the present inventors are co-inventors, a process is described, according to which carbonyl compounds can be obtained from the corresponding olefins in a good yield, and, if desired, in a continuous manner by contacting said olefins with gaseous oxygen, water which is present in the vaporous form, and a solid catalyst which contains a compound of a noble metal belonging to group VIII of the periodic system as catalytic substance and a redox system.

Finally it is described in application Ser. No. 760,539 filed September 12, 1958, and now Patent No. 3,057,915 in which two of the present inventors are co-inventors, that the yield of acids which correspond to the aldehydes can be considerably increased without the aldehyde yield being reduced when an olefin is contacted with gaseous oxygen in the presence of water vapor and a solid acid to neutral catalyst containing a carrier, a compound of a noble metal of group VIII of the periodic system and a redox system containing one or more compounds of one or more metals having an atomic number in the range from 25 to 27, i.e. iron, manganese, and/or cobalt.

In the aforesaid applications the term carbonyl compounds is used in its broad sense, i.e. it covers not only aldehydes and ketones, but also carboxylic acids such as acetic acid.

It has been mentioned in the aforesaid applications that the reactants may be diluted by gases inert towards the reaction, for example by nitrogen, carbon dioxide, methane, ethane, propane, butane, isobutane and other saturated aliphatic compounds and furthermore by other compounds such as cyclohexane, benzene or toluene.

We have now found that the olefins may not only be diluted by one or more of the aforementioned gases, but surprisingly likewise by carbon monoxide and/ or hydrogen. It has unexpectedly been found that the presence of these gases does not affect the course of the reaction. If such gas mixture contains CO, oxygen should be present at least in an amount as is necessary to convert the olefin to aldehyde and carbon monoxide to carbon dioxide.

It is believed that olefin-noble metal complex compounds are formed as intermediary products which then react with water to yield carbonyl compounds. It is, however, known from the literature that carbon monoxide expels from these coordination compounds all olefins, including ethylene. For these reasons a mixture of olefins with carbon monoxide was expected to bring about no or only a very small conversion of the olefin to carbonyl compounds. It is therefore surprising that a mixture of carbon monoxide and olefin, if desired in admixture with one or more other gases inert towards the reaction, such as those mentioned above, practically yields the same amounts of carbonyl compounds as if no carbon monoxide were present. In this reaction the carbon monoxide is partiaily converted to carbon dioxide.

It is also known from the pertinent literature that hydrogen reacts in a manner very similar to that of carbon monoxide, and it is therefore just as well surprising that the olefin oxidation takes an absolutely smooth course in the presence of hydrogen. The major amount of hydrogen remains unaltered, whereas a small portion thereof reacts with formation of water and another small portion with hydrogenation of the olefins.

The carbonyl compounds can be obtained in the same manner without a reduction in conversion occuring by using a mixture of carbon monoxide and hydrogen with an olefin or a gas containing an olefin; in this case, it

is sometimes favorable for the conversion to work with the application of pressure.

The fact that neither hydrogen nor carbon monoxide affects the process of the invention is of special advantage since accordingly industrial gases, for example refined gases or gasses obtained in cracking processes, may be used as starting materials. All expensive gas separations can therefore be dispensed with, although a prepurification or concentration of the olefin may provide advantageous, so that a considerably cheaper crude material can be used. Carbon monoxide and/or hydrogen may appear in the gas mixture, for example in double the amount of the olefin, and yet the olefin oxidation is not substantially impaired. This statement is, however, not intended to indicate a limit. If these gases are present, it is especially suitable to use the multiple stage process described in application Ser. No. 750,150, in which the olefin, if desired in admixture with a small amount of oxygen, is contacted with the catalyst in one stage, while the oxidizing agent is contacted with the catalyst in a second stage or apparatus. This modification of the present process is broadly described below. As a result of these measures it is possible to practically avoid a mixing of the gases used with oxygen, so that the former can be used for further purposes after having left the reactor.

The reacted gases may-advantageously after they have been freed from the reaction productsbe recirculated, or, if no or small amounts of olefins are present, may be used for other purposes.

The process of this invention may be carried out wit-h catalysts and under the conditions broadly described in applications Ser. No. 747,116, 750,150, 747,115 and 760,539 and referred to above.

There may be used as redox systems, for example, those that contain compounds of metals which under the reaction conditions employed may appear in various oxidation stages, for example compounds of copper, mercury, cerium, thallium, tin, lead, titanium, vanadium, antimony, chromium, molybdenum, uranium, manganese iron, cobalt, nickel, or osmium, and also inorganic redox systems other than specified above, such as sulfite/sulfate, arsenite/arsenate or iodide/ iodine systems and/ or organic redox systems, for example azobenzene/hydrazobenzene, or quinones or hydroquinones of the benzene, anthraceneor phenanthrene series.

As compounds of the noble metals of group VIII of the peirodic table there may be used in the process according to the present invention, for example, compounds of palladium, iridium, ruthenium, rihodium or platinum. Compounds of this series of metals are believed to be capable of forming addition compounds or complex compounds with ethylene. The reaction may likewise be carried out in the presence of a noble metal.

As oxidizing agent there may be used, for example, oxygen, if desired in admixture with an inert gas. The oxygen may be employed, for example, in the form of air, which is the cheapest oxidizing agent or in the form of air enriched with oxygen. The use of air is, however, confined to certain limits, if the unreacted gases are circulated, inasmuch as nitrogen concentrates as ballast material.

The reaction may be supported or carried out by addition of an active oxidizer, such as ozone, peroxidic compounds, especially hydrogen peroxide or sodium peroxide, potassium peroxide, potassium persulfate, ammonium persulfate, alkali percarbonate, alkali perborate, peracetic acid, diacety-l peroxide, benzoyl peroxide, toluyl peroxide, oxygen compounds of nitrogen, such as nitrogen dioxide and nitrogen pentoxide or mixtures of nitrogen oxides containing the same, nitryl halides such as nitryl chloride, free halogen such as chlorine, bromine, or bromotrichloride, halogen-oxygen compounds such as chlorine dioxide, hypochlorous acid, chloric acid, perchloric acid, bromic acid, iodic acid, periodic acid, or compounds of the higher valene stages of metals, such as manganese, cerium, chromium, selenium, lead, vanad um, silver,

molybdenum, cobalt, or osmium, for instance potassium permanganate, sodium bichromate, lead tetraacetate, vanadium pentoxide, silver difiuoride, selenium dioxide, cerium-(IVlsulfate, osmium tetroxide. The addition of an active oxidizer facilitates the re-formation of the higher oxidation stage of the active catalyst component which is necessary for carrying out the reaction. These oxidizing agents may also be produced during the reaction. If desired, an oxidizing catalyst may be added. It is often advantageous to add, prior to or during the reaction, a compound yielding anions under the reaction conditions applied, for example an inorganic acid, preferably a mineral acid such as sulfuric acid, nitric acid or a volatile acid, such as hydrochloric acid or hydrochromic acid, or a salt such as ammonium chloride, ammonium bromide, zinc chloride, aluminum chloride, iron chloride, chromic chloride, titanium tetrachloride, sodium hydrosulfate, a halogen or a halogen-oxygen compound, for example those mentioned above, or thionyl or sulfuryl chloride, or also an organic substance, preferably a saturated aliphatic halogen compound of low molecular weight such as ethyl chloride, propyl chloride, butyl chloride, acetyl chloride, benzoyl chloride, propionyl chloride, phosgene. Such addition enables a possible decrease of anions to be counteracted and the lifetime of the catalyst to be prolonged.

In case that the reaction is carried out in the presence of solid catalysts and that non-volatile compounds yielding anions are used as listed above, these substances are, of course, added to the catalyst before the reaction, while the volatile compounds can be added as well before as during the reaction.

The process of the present invention is carried out at relatively low temperatures and may be carried out as well in the presence of a solid catalyst as in solution. If solid catalysts are used, suitable contact supports (carriers) are, for example, silica gel, kieselguhr, pumice, silicates, TiO A1 0 active carbon, acid ion exchangers, such as Amberlite IRC 50, Dowex types 50, Permutites, phenol-aldehyde-resins which are substituted by sulfonic acid groups, polystyrene-resins which are substituted by sulfonic acid groups and crosslinked by divinyl-benzene etc., or mixtures of such carriers.

If liquid catalysts are applied, preferably a pure aqueous solution is used, but the reaction may likewise be carried out in aqueous solutions in which the water is diluted With a hydrophilic solvent such as acetic acid, acetone, methylethyl ketone or other ketones, ethylene glycol, propylene glycol, glycerol, dioxane or mixtures thereof.

The present process can be carried out with special advantage at temperatures within the range between 50 and C., preferably 50 and 100 C. if it is carried out in the liquid phase, it is necessary to operate under a raised pressure provided that the temperature used is above 100 C. If desired, the process may also be carried out at temperatures outside the ranges indicated above, for example at C. to C., or for example at 40 C., or within a range of, for example, 80 C. to 120 C. It is furthermore of importance to carry out the process in an acid to neutral medium. The preferred pH-val-ues are within the range between 0.8 and 3; higher pH-values between, for example, 0.8 and 5 or 2 and 6, or lower pH-values, for example, 0.5 may also be used, although such pH-values generally do not involve a special advantage. If solid catalysts are used the solution with which the solid catalyst is impregnated may be adjusted so as to have a pH within the limits indicated above.

Difficulties which may appear in working in the liquid phase can be overcome by modifying the ratio of olefin to oxygen. Such difficulties may reside in the precipitation of cuprous chloride or other compounds formed which cause cloggings and undesired disturbances in operation. In view of the fact that these precipitated salts are no longer available for the reaction, the yield decreases more or less rapidly. The moment at which the olefin to oxygen ratio must be modified, can be readily determined by continuously measuring the pH.

If the pH decreases, it is easily possible to readjust the optimum pH-range by adding either more oxygen or less olefin, or by combining these two steps. If the pH increases, the optimum pH-range can be readjusted inversely. This method of controlling the reaction may also be combined with the above described addition of com pounds yielding anions, for example hydrohalic acid or organic compounds splitting off hydrohalic acid under the reaction conditions, or acid salts. It is especially advantageous to adjust the reaction medium to a certain pH at the onset of the reaction, for example by means of hydrochloric acid, and to regulate the olefin-oxygen ratio during the reaction. The pH may of course also be modified during reaction by addition of an acid.

The pH is measured by using a device of known type. The pH may be measured continuously with electrodes arranged in the reactor, or discontinuously by measuring the pH of samples withdrawn in certain intervals of time. In a special technical variant of this method the pH-measuring device has an automatic connection to the dosing device for the supply of ethylene and oxygen. In this case the pH is once adjusted to the optimum value and the reaction can then be controlled automatically.

Sometimes the presence of a salt, such as sodium chloride or potassium chloride may prove advantageous. For example, by the presence of these saltslike that of hydrochloric acid itself or of other alkali metal or alkaline earth metal halides such as LiCl, CaCl MgCl or other salts such as FeCl ZnCl or CuCl -the solubility of CuCl, which may be formed in the course of the reaction and which is only very sparingly soluble in water (0.11% at 80 C.) is improved. In solid catalysts the reactivity of CuCl may for instance be improved by'the presence of such salts.

The present process can be carried out at atmospheric pressure, under a raised pressure or under reduced pressure, that is, under a pressure of up to 100, preferably of up to 50 atmospheres gauge. The process may be carried out under pressure regardless of whether the temperatures used are above or below 100 C.

The reaction may be supported by increasing the ethylene and/or oxygen concentration in the reaction space. This can be achieved, for example, by increasing the pres sure and/or-especially, when the reaction is carried out in the liquid phaseby the presence of a solvent. The ethylene concentration in the reaction solution may be considerably increased, for example, by using higher concentrations of metal salts binding ethylene, for instance copper-, ir0n-, mercuryor iridium compounds, especially halides, or the sulfates, the latter especially when mercury is concerned, or by using organic solvents which are preferably miscible with water, for example acetic acid, methylethylketone or other ketones, monoor polyhydric alcohols, acyclic ethers or dimethyl formamide. The gases may be circulated, if desired, for example as gas containing a few percent of unreacted oxygen.

Due to the presence of oxidizing agents acetic acid may be formed in a small amount in addition to acetaldehyde. If desired, the oxidation of acetaldehyde to acetic acid which is known in the art, may be combined with the reaction described above in order to omit partially or totally the aldehyde stage, or acetaldehyde may be oxidized in a second stage to acetic acid.

Under the conditions specified above under which ethylene yields acetaldehyde, propylene yields preponderantly acetone and propionaldehyde. a and ,B-butylene yield preponderantly rnethy-lethyl ketone, the wbutylene yielding also butyraldehyde, and isobutyraldehyde can be obtained from isobutylene.

In the case where higher olefins are concerned, such as pentene and its homologs, cyclohexene or styrene, the reaction proceeds substantially in a manner analogous to that described and it can be carried out under the same action conditions, for example diolefins.

conditions as set forth above. Due to the relatively mild reaction conditions there are almost exclusively obtained those oxidation products which had to be expected in view of their structure, without noteworthy isomen'zations or molecule decompositions occuring.

Mixtures of olefins or gases containing olefins or other unsaturated compounds may be reacted in the same manner, provided they are capable of reacting under the re- The reaction of olefins containing 2 to 3 carbon atoms is however preferred. Under circumstances, the reaction conditions must be adapted to the compounds used and to their physcial properties. The higher boiling points of the reaction products may also require a corresponding modification of the reaction conditions. Diacetyl may be obtained, for example from butadiene.

For stoichiometric reasons the molar ratio of olefinic bond to oxygen must be 2:1 in the complete oxidation of olefins to the corresponding aldehydes or ketones. To prevent explosions, it is, however, preferred to use an oxygen deficiency, for example in the range of 2.5:1 to 4:1. Still further it is preferred to work outside the range of explosivity, for example with a content of oxygen of 8-20%, or 814% under pressure, and to circulate unreacted gas which consists substantially of non-converted olefin, hydrogen and/ or carbon monoxide, and, if desired containing other inert gases such as nitrogen, and may furthermore contain some oxygen. To this gas oxygen and the olefin, such as ethylene are restored as they are consumed.

The present process may be carried out for example by contacting the olefin which is diluted with hydrogen and/ or carbon monoxide and oxygen or air simultaneously with the catalytic substances. However it is often very advantageous, especially if liquid catalysts are applied, to contact the olefinic and the oxidizing agent separately with the liquid catalyst used. This mode of operating has the advantage that the composition of the gas mixture need not be controlled carefully and that even in recirculating the olefinic reactant, such as an ethylene containing gas, air may be used as oxidizing medium without disadvantages being involved. This variant may be performed by contacting the olefinic gas mixture and the oxidizing agent in periodic alternation with the circulating catalyst liquid in a vessel; in a continuous operation there may be used to this end a reciprocally reversible double apparatus, or the olefinic gasmixture and oxidizing agent are contacted with the circulating catalyst liquid in several reaction vessels. In this variant, the olefinic gas mixture may still contain oxygen, the oxygen content being outside the range of explosivity, i.e. for example, between 1% and 10%, preferably between 3% and 10% of oxygen, calculated upon the amount of olefin used. For example, the explosive limit of .an ethylene-oxygen gas mixture is at atmospheric pressure at 20.1% of oxygen. In this modified variant the reaction is preferably carried out in such a manner that the oxygen is almost or completely consumed in the reaction vessel and the catalyst is then regenerated in the regeneration vessel. In this vessel the contact medium is contacted in a further separated stage with the oxidizing medium in an amount sufficient to bring about regeneration, for example oxygen or air. Regeneration is brought about under known con ditions, for example at 50-150 C. and may be carried out under pressures and at temperatures being different from those of the first stage in which the catalyst is contacted with the olefin.

Depending on the conditions applied in this case the olefin dissolved in the catalyst medium is also oxidized and the dissolved reaction product is removed 'by stripping. In order to produce a good stripping effect, regeneration may also be brought about using mixtures of oxygen or air with steam.

Contacting the olefinic gas mixture and the oxidizing agent separately with the contact medium involves the '2 advantage that the process can always be carried out under atmospheric pressure and, more especially, under su peratmospheric pressure, with gas mixtures which are outside the inflammability limit and absolutely harmless.

As compared with the variant to contact the olefinic gas mixture per se and the oxidation agent per se with the contact medium, the use of an olefinic gas mixture containing a small amount of oxidizing agent in one stage and of additional oxidizing agent in the second stage offers the further advantage that an occasional separation of undesired solid products is avoided at the place where an oxygen containing, olefinic gas mixture enters into the reactor, which contains oxygen in an amount smaller than corresponds to the stoichiometric composition as regards the conversion to the carbonyl compound, and the composition of which gas mixture is outside the inflammability limit. A separation of solid substances would cause reduction of the catalytically active substance in the contact liquid and accordingly a reduction of the contact activity; on the other hand, such separation would involve cloggings in conduits, cocks or nozzles. Such separation of solid substances does not appear if the olefin gas mixture contains a minor amount of oxygen or air and such mixture is contacted in the first stage with the contact solution, and if the con-tact solution is regenerated in a second stage :by addition of a further amount of oxidizing agent. If the olefinic gas mixture and the oxidizing agent, or an olefinic gas mixture containing a small amount of oxygen and the oxidizing medium, for example oxygen, are contacted separately in the manner described above with the catalyst, it may be advantageous to free the olefin-treated contact solution before it is being contacted in a second phase with the oxidizing gases, from residual unreacted olefin and residual reaction product, for example by stronger heating or stripping with an inert gas, such as nitrogen or steam. By connecting the head of the reaction tower of one phase with the lower liquid inlet of the regeneration tower and vice versa, it is possible to produce a closed liquid cycle, so that pumps can be dispensed with. The ascending gas currents circulate the liquid vigorously; this circulation can be measured by flow meters or another suitable device.

If it is feared that the mixture comprising residual oxygen or residual air and aldehyde, for example acetaldehyde, could rise slightly above the lower explosive limit, the head of the regeneration tower may readily be provided with a safety device of known type to prevent explosion, such as lbursting disks, a breakdown security device (gravel pots) or the like. The danger of explosion is however extremely low in view of the acetaldehyde-oxygen-mixture being saturated with water vapor and in view of the relatively low content of oxygen, which is smaller than the oxygen content of the air.

The present process may, e.g. be carried out in an apparatus shown in the appended drawing. A current of an olefinic gas mixture is introduced through a compressor 1 into reactor 2 or 2a in concurrent or countercurrent to the catalyst liquid, and the gas is finely distributed in the catalyst solution by means of a suitable device, for example a frit, a mixing nozzle, an oscillatory sieve, a vibrator, a rapid agitator or the like.

The olefin is converted in this solution to a carbonylcontaining reaction product leaving the reactor together with unre-acted olefin and diluting gas, if desired via a cyclone 3. The reaction product is separated in a separating device 4 from the remainder of the olefinic gas mixture, which latter substance may then be recirculated together with a fresh amount of olefin into the reactor via compressor 1 if it still contains substantial amounts of olefin, or may be used for other purposes. The reaction liquid is then conducted to a stripper 5, where it is treated with steam to be directly or indirectly freed from olefin and residues of reaction product. The gases obtained by stripping are conducted, if desired, to separating device 4. The stripped reaction solution is then introduced into regenerator 7 by means of a pump 6 or a static incline. The stripping stage may, however, be omitted, and the reaction solution is then directly introduced into regenerator '7. The solution is intimately contacted in generator 7 with oxygen or gases containing oxygen. The regenerator may be designed so that the contact liquid flows in a countercurrent to the oxygencontaining gases, which leave the regenerator through cyclone 8, and may be returned into the cycle by means of a compressor. The contact liquid is then communicated in the regenerated state to reactor 2 or 2a by means of pump 9. All partial operations may be carried out individually or together at a raised pressure, at a reduced pressure, or at atmospheric pressure.

The aforesaid two-stage embodiments have the mutual advantage, that explosive gas mixes are not liable to occur even when operating under a raised pressure, and that each gas current can be circulated separately and replenished by fresh gas to the necessary extent. It is also possible to use air as oxidizing agent in view of the fact that a concentration of nitrogen has here no detrimental effect.

If it is intended to prepare large amounts of acids which correspond to the aldehyde simultaneously with other carbonyl compounds, such as aldehyde, a mixture of olefin with hydrogen and/ or carbon monoxide is contacted with gaseous oxygen if desired in the form of air in the presence of water vapor at a solid acid to neutral catalyst comprising a carrier, a compound of a noble metal of group VIII of the periodic system and a redox system containing one or more compounds of one or more metals having an atomic number in the range from 25 to 27, i.e. iron, manganese and/or cobalt.

The compounds of iron, manganese or cobalt are added to the catalyst in the usual manner. It is possible, for example, to impregnate the catalyst with the soluble salts of these elements and to convert these salts by heating, preferably with air, to the firmly adhering oxides. There may also be used a mixture comprising the aforesaid compounds.

The acid formed can be readily separated from the corresponding aldehyde. It is preferred to concentrate the acid, which has always a boiling point higher than the aldehyde, in a first separator, and to concentrate the aldehyde which has a boiling point lower than the acid, in a second separator. Both separators are connected in series.

The simultaneous production of carboxylic acids and aldehydes at solid catalysts containing an iron-, manganeseand/or cobalt salt, is preferably carried out in the presence of further redox systems, such as copper compounds.

In a frequently useful technical variant of the process of this invention, the desired reaction product, for example acetaldehyde, and, if desired, acetic acid, is separated from the reaction gas, the residual gas which may still contain hydrogen and/ or carbon monoxide and furthermore inert gas and may be free from oxygen, but may likewise contain oxygen, is reintroduced into the reactor, suitably into its lower part and an amount of olefin and if desired oxygen corresponding to that consumed during the reaction is introduced into the reactor through one or more inlets which may be arranged one above the other or one behind the other, or the olefin and/ or the oxygen are added to the recirculated gas. For example, the ethylene or, if the olefinic gas mixture used contains but small amounts of diluting gas, e.g., 1% to 10% by volume of hydrogen and/ or carbon monoxide, ethylene-containing gas is admixed with the residual gas in amount corresponding to that consumed. The resulting gas mixture which may be free from oxygen or in which the ratio of olefin and oxygen is, for example 95 to 99 percent or to percent of olefin (for example ethylene) to 5 to 1 percent or 10 to 5 percent, respectively of oxygen, is then introduced into the reactor. For the sake 9 of security the oxidizing agent, i.e. preferably oxygen, if desired in admixture with inert gases, such as present in air, is preferably introduced through separate inlets, especially when about stoichiometric amounts of the reactants are applied.

Preferably the oxidizing agent is introduced below the inlet for the residual gas or, if a circulating cataylst is used, into the circulation conduit of the catalyst. The amount of oxygen introduced may be so modified that even in the catalyst solution the explosivity limit is nowhere surpassed, Such modification is generally not necessary; it is rather sufficient to add the oxygen to the residual gas which escapes from the contact solution, in an amount to keep the composition of this residual gas outside the explosive limits.

In order to obtain especially high space-time-yields, it is also possible to introduce either olefinic gas mixture or oxidizing agent, preferably oxygen, or olefinic gas mixture and oxygen into the reaction vessel, for example a reaction tower, at various places arranged one above the other or one behind the other. Preferably the inlets for each reactant are locally separated from the other inlets for the same reactant. It is likewise possible that the amount of oxygen introduced is measured so as to kee at all places of the reaction vessel below the lower limits of the explosive range.

If the reaction is carried out in the presence of liquid catalysts it may be advantageous to add a dispersant, for example an alkylphenyl sulfonate or a product obtained by the reaction of ethylene oxide, propylene oxide, or

- butylene oxide with phenols or aliphatic alcohols, and/ or a protective colloid, such as proteins or gum arabic to the liquid catalyst. Finely dispersed solid substances may also be added, if desired. The activity of these substances resides in the fact that free noble metal which has intermediately formed and is reconverted into active compounds by the reactants used in the instant process, cannot aggregate to form large particles. The cataylst is therefore especially finely distributed, and the degree of distribution is stable. As solid pulverulent substances there may be used, for example, charcoal powder or kieselguhr. It is also possible to use a combination comprising dispersant, protective colloid and finely distributed solid substance.

In many cases the reaction proceeds likewise smoothly if the catalysts used contain only a small amount of compounds of the noble metals belonging to group VIII of the periodic table. In most cases it is sufficient to use a cataylst in which the ratio of the sum of the redox metals, especially the sum of copper and iron to the noble metal, especially palladium, is at least 15:1, preferably 25-500I1. It is, however, preferred to use a catalyst containing copper salts, in which the ratio of copper to palladium is above 10:1, for example above :1 and preferably 50:1 to 500:1, or even above these ranges. This method of operating is more economic in view of the fact that the expensive palladium salt need only be used in a minor amount; it can be used for converting ethylene and olefins other than ethylene, and may be combined as desired with variants hereinbefore or hereinafter described. This embodiment may also be carried out under elevated pressure.

The halogen content of the liquid catalysts used in the present reaction may become depleted in the course of time, a fact which possibly causes a reduction in the rate of conversion. The loss of halogen may be counteracted by addition of halogen or hydrohalic acid or organic substances splitting off halogen or hydrohalic acid under the reaction conditions as already stated.

Such depletion of halogen is to be attributed substantially to the formation of volatile halogenated lay-products, for example methyl chloride or ethylchloride, which together with the carbonyl compounds produced entrain the halogen from the catalyst more or less rapidly. It has been ascertained that a certain amount of carboxylic acid corresponding to the olefin, is produced during the reaction, for example acetic acid; such acid concentrates in the liquid and increases the solubility of the reaction products. This favors the formation of halogen-containing volatile by-products and promotes the depeltion of halogen. In addition thereto, the carboxylic acids which have concentrated, especially acetic acid, react with the copper ions, which is unfavorable because the copper salts formed, such as copper acetate, are relatively inert towards the olefin oxidation. In many cases it is therefore necessary to counteract such accumulation of carboxylic acids in the reaction space and to take care that these acids appear in as low a concentration as possible. This may be done by suitable continuous or discontinuous measures, for example by distillation, extraction or precipitation. A preferred variant in operating under atmospheric pressure consists, for example, in that the car- 'boxylic acids formed are allowed to distill over together with the evaporating water; the water consumed is then replaced by a corresponding amount of fresh water. The amount of carboxylic acid removed in this manner is dependent on the surface of the reactor, the temperature used and the amount of gas flowing through, and may be modified by varying these factors. According to another variant the entire contact solution is worked up, carboxylic acid contained in the catalyst is removed, and the contact solution is recirculated into the apparatus.

In order to avoid operative disturbances part of the contact liquid may be withdrawn periodically or continuously and freed from carboxylic acid, partially or substantially, for example by distillation, and the liquid obtained may be added again to the contact medium. The reaction of the present invention is favorably influenced by irradiation with rays rich in energy, preferably ultraviolet light, especially in the case where oxygen is used as oxidizing medium. Such radiation which may also comprise X-rays activates especially the oxygen, increases its oxidizing activity, and promotes both the reaction With the olefin and a possible oxidative destruction of -by-products, for example oxalic acid. These measures increase the conversion, reduce the formation of byproducts and considerably prolong the lifetime of the catalyst, the activity of which may subside after a prolonged time.

In practice it is advantageous to use a mercury quartz lamp as source of radiation arranged in the catalyst so that the light energy is fairly substantially utilized. If the reaction is carried out with an apparatus into which oxygen or an oxygen-containing gas is introduced separately from the olefinic gas mixture or even a mixture of the said reactants, it is preferred to arrange the source of radiation in the vicinity of the oxygen inlet, so that that part which is rich in oxygen is especially well irradiated. The oxygen is thereby activated as long as it has a high partial pressure. In the present process, especially in an apparatus, in which the catalyst is circulated it is advantageous to arrange the source of radiation at the lower end of the conductline or, if the reactant is carried out in several stages, at the lower end of the regeneration vessel, immediately above the oxygen inlet. Activation may also be brought about by adding a compound of a radio-active element to the catalyst solution.

It is known that at a constant volume of the reaction liquid and in the case Where the reaction does not run completely in one direction, the rate of conversion is the better, the higher and narrower the design of the reactor. It is also evident that such reaction proceeds the better, the finer the gaseous components are distributed in the liquid. The catalyst solutions suitable for use in the process of this invention have sometimes the property of foaming after sometime. On the one hand this favors the reaction in view of the fact that the gases are finely distributed in the catalyst liquid; sometimes foam-forming agents are intentionally added to the liquid. On the other hand, foaming means that the reaction space available is only insufliciently used, since only part of the contact solution is in the reactor.

The process of this invention may be carried out for example in vertically arranged tubes provided with frits or oscillatory agitators. The process may also be carried out in usual reaction towers, for example wash towers, suitably filled with filling material. The gases may be atomized, for example through a frit, or in another suitable manner, and too voluminous gas bubbles may be divided into smaller ones, for example by means of an agitator. For this purpose there may also be used a vibro-mixer or a turbo-mixer. All these variants enable the reaction to be carried out continously.

The conversion and the space/time/yield depend for example, on the residence time in the apparatus, and the composition of the catalyst, the temperature and the pressure used, and, if liquid catalysts are used, furthermore on the fine distribution of the gas. The most suitable residence time can readily be determined by a simple test.

In the process of this invention advisably care is to be taken that the heat evolved during the process (high heat efiect: about 60 kcal. per mole of aldehyde) is dissipated to the exterior.

The reaction of the present invention may be carried out in a manner known per se, for example by passing the gases through a tube which is filled with the catalyst, or with the use of a fluidized bed catalyst. Condensates which separate from the reacted gas, especially aqueous condensates, may also be recirculated. If solid catalysts are used, they are of course vaporized to again participate in the reaction, for example as such or after separation of higher and/ or lower boiling reaction products.

It is not necessary that the catalysts used are made of fine chemicals; they may likewise be produced from suitable metals of commercial purity. Metals such as copper and iron may be readily dissolved even by nonoxidizing acids, such as hydrochloric acid and acetic acid, if desired by addition of an oxidizing agent, especially if copper is used, or by passing through during the dis solving process as gaseous oxidizing medium such as oxygen or air enriched with oxygen. The contaminations contained in commercially pure metals do not affeet the reaction if the solutions obtained are used as catalysts or are Worked up to the solid bed catalysts for the olefin oxidation. More especially, the catalytic activity remains practically unaffected by small amounts of foreign metals which may appear in copper or iron of commercial purity. The anion forming agents contained in metals, such as sulfur, phosphorus, carbon, silicon etc. are converted upon being dissolved to either hydrogen compounds, for example H 8, which escape together with the reaction gases, or oxidized to acids of a higher valence stage, for example H 50 which do not affect the reaction, or converted partially into insoluble compounds, for example CuS, which appear only in minor amounts and, if necessary, can readily be separated from the catalyst, for example by filtration, before the catalyst is used or the catalyst solution is applied to a carrier.

The solutions so obtained are then admixed with the noble metal compound which is added in substance or in the dissolved state, if desired diluted with water, and the concentration of hydrogen ions is adjusted to the degree desired; the solution so prepared may then directly be used as a catalyst for the olefin oxidation in the liquid phase or they may be concentrated and be applied to a carrier, for instance, to those mentioned above.

Solvents suitable for dissolving the metals are chiefly hydrochloric acid and acetic acid in view of the fact that the presence of these acids proves especially advantageous in oxidizing olefins to aldehydes, ketones and acids. Acids other than those indicated above may, however, also be used, for example nitric acid. In this case, it is preferred to remove the acid in excess in order to adjust the solution to the pH desired and to use the solution so treated as a catalyst or for impregnating the carrier. If desired the salt of the metals may also partially be converted into the corresponding chlorides and/ or acetates.

Palladium chloride or other noble metal chlorides need not be used, since there may also be employed the metals themselves, e.g. metallic palladium, suitably in a finely divided and finely distributed state, which reacts, for example, with copper chloride, and is converted to palladium chloride or a compound other than palladium chloride.

For example, the catalyst may contain as anion chlorine ions or halogen ions other than chlorine, such as fluorine or bromine ions, nitrates or chlorateor per chlorate radicals or mixtures of these anions, for example, with sulfate or acetate radicals. Sometimes it is especially advantageous to use a catalyst which contains perchlorate ions.

Although the catalysts have generally a good activity even after a prolonged time of reaction, especially when anions are added during the reaction, it may be advantageous to regenerate the catalyst from time to time. Such regeneration methods are described hereinafter. Some further variants of regeneration methods have been described in the above-cited applications.

A possibility to recover palladium metal from liquid catalysts consists in subjecting the catalyst in known manner and in a strong acid medium to the action of acetylene. A palladium-acetylene compound precipitates which can be readily separated and freed from cations and anions by means of a water wash. The palladiumacetylene compound so obtained may be then converted in the air or in the presence of ammonium nitrate to palladium oxide which in turn is capable of being converted directly to the chloride by means of hydrochloric acid. In this variant it is especially advantageous that acetylene can act on the palladium compound in the presence of hydrogen.

According to another method a solid bed catalyst may be regenerated by arresting the olefin supply for a short while and treating the catalyst simultaneously with oxygen or oxygen-containing gases and steam and an acid in vapor form or gas form, preferably hydrogen chloride or hydrogen bromide. A variant of such regeneration consists, for example, in passing oxygen or an oxygen-containing gas partially or completely and prior to contacting the catalyst through aqueous hydrochloric acid, preferably at a raised temperature. Accurately dosing the hydrochloric acid is especially simple, if a 20 percent hydrochloric acid is used.

The catalyst which prior to this treatment has possibly a metallic lustre turns again brown and regains its initial activity, possibly after an induction period of several hours.

The apparatus used in the process of this invention should be made of a material which is not corroded by the catalyst and preferably especially if solid catalysts are used, has a sufiicient thermal conductivity. Since the catalysts used contain noble metal compounds, for example palladium compounds, it is less suitable to use the usual metals and alloys as construction material, since there is the risk that these less noble metals, in the presence of water and at the indicated temperatures, precipitate the noble metal salt used in the catalyst, and that they themselves are converted into salt form.

In order to avoid corrosion in the apparatus used, it is often suitable to use an apparatus lined with titanium or titanium alloys containing at least 30 percent of titanium, or with tantalum. There may also be used glass vessels or enamelled or rubber-lined vessels. The reaction may also be carried out in brick-lined vessels or, under suitable reaction conditions, in vessels the insides of which are lined with plastic material, for example polyolefins, polytetrafiuorethylene or hardenable unsaturated polyesters, or phenol-, cresolor xylenol-formaldehyde resins.

As brick lining there may be used, for example, ceramic material, carbon Ibricks impregnate-d with hardenable artificial resins and similar known materials.

The following examples illustrate the invention but they are not intended to limit it thereto.

Example 1 50 cc. of a catalyst solution containing, per liter of water, 1 gram of PdCl 100 grams of CuCl -2H O, and 5 cc. of concentrated hydrochloric acid, are heated to 80 C., and 1.5 liters of :gas are passed through per hour. The gas used consists of 50% of ethylene and 50% of carbon monoxide and is mixed with half its volume of oxygen prior to the reaction. The formed acetaldehyde is separated from the reaction mixture by Washing. The conversionycalcultaed upon the ethylene used, is above Example 2 A gas consisting of 10% of hydrogen, 20% of methane, 35% of ethane and 35% of ethylene, to which half its volume of oxygen has been admixed prior to the reaction, is introduced under the conditions described in Example 1 into the catalyst solution. The conversion to acetaldehyde calculated upon the ethylene used, is at about 5 Example 3 A gas consisting of 10% of hydrogen, 10% of carbon monoxide, 30% of methane, and 50% of ethylene, to which half its volume of oxygen has been admixed prior to the reaction, is introduced into the catalyst solution under the same conditions as described'in Example 1. The conversion to acetaldehyde calculated upon the ethylene used, is above 40%.

Example 4 Example 5 100 cc. of an aqueous catalyst solution containing 0.2 gram PdCl and grams CuCl -2H O were introduced into a vertically arranged tube and maintained at 90 C. by jacket heating. 5 liter/h. of a mixture consisting of 70% by volume propylene, 20% by volume CO and 10% by volume propane and 2.5 liter/h. oxygen were then introduced into the tube through a frit and passed through the above catalyst solution.

The resulting acetone which contained traces of propionaldehyde was then washed out in a washing column.

The reaction was maintained by adding at intervals of about 2 hours 1 cc. 0.5 N-hydrochloric acid. The conversion rate per passage through the catalyst solution was about 32%, calculated on propylene.

We claim: 4

1. In a process for conversion of an olefinic hydrocarbon to a carbonyl compound selected from the group consisting of aldehydes and ketones by oxidizing an olefinic carbon atom of said olefinic hydrocarbon to a carbonyl group by contacting said olefinic hydrocarbon and oxygen at a temperature between 50 C. and C. and at a pH between 0.5 and 6 with water and a catalyst of (a) a salt of a noble metal selected from the group consisting of palladium, iridium, ruthenium, rhodium and platinum and (b), as a redox system, an inorganic salt of a metal showing several valence states under the reaction conditions applied, the improvement of contacting said olefinic hydrocarbon, oxygen, and said catalyst in the presence of a diluent gas selected from the group consisting of carbon monoxide and hydrogen.

2. A process as in claim 1, wherein said catalyst is contacted in a first stage with a gas mixture comprising an olefinic hydrocarbon and carbon monoxide as a diluent, and said catalyst and oxygen are then contacted in a second stage in the absence of substantial amounts of said olefinic hydrocarbon and diluent gas.

3. A process as in claim 1, wherein said catalyst is contacted in a first stage with a gas mixture comprising an olefinic hydrocarbon and hydrogen as a diluent, and said catalyst and oxygen are then contacted in a second stage in the absence of substantial amounts of said olefinic hydrocarbon and diluent gas.

4. A process as in claim 1, wherein said diluent gas is hydrogen.

5. A process as in claim 1, wherein said diluent gas is carbon monoxide.

6. A process as in claim 1, wherein said diluent is a mixture of hydrogen and carbon monoxide.

References Cited by the Examiner UNITED STATES PATENTS 3,027,411 '3/ 1962 Murphy 260-604 3,076,032 1/ 1963 Riemenschneider et al.

260-604 3,119,875 1/1964 Steinmetz et a1. 260-604 FOREIGN PATENTS 228,831 6/ 1960 Australia. 1,210,009 3 1960 France.

638,754 6/ 1950 Great Britain.

LEON ZITVER, Primary Examiner.

CHARLES B. PARKER, Examiner.

B. HELFIN, J. J. SETELIK, Assistant Examiners. 

1. IN A PROCESS FOR CONVERSION OF AN OLEFINIC HYDROCARBON TO A CARBONYL COMPOUND SELECTED FROM THE GROUP CONSISTING OF ALDEHYDES AND KETONES BY OXIDIZING AN OLEFINIC CARBON ATOM OF SAID OLEFINIC HYDROCARBON TO A CARBONYL GROUP BY CONTACTING SAID OLEFINIC HYDROCARBON AND OXYGEN AT A TEMPERATURE BETWEEN 50*C. AND 160C. AND AT A PH BETWEEN 0.5 AND 6 WITH WATER AND A CATALYST OF (A) A SALT OF A NOBLE METAL SELECTED FROM THE GROUP CONSISTING OF PALLADIUM, IRIDIUM, RUTHENIUM, RHODIUM AND PLATINUM (B), AS A REDOX SYSTEM, AN INORGANIC SALT OF A MEAL SHOWING SEVERAL VALENCE STATES UNDER THE REACTION CONDITIONS APPLIED, THE IMPROVEMENT OF CONTACT ING SAID OLEFINIC HYDROCARBON, OXYGEN, AND SAID CATALYST IN THE PRESENCE OF A DILUENT GAS SELECTED FROM THE GROUP CONSISTING OF CARBON MONOXIDE AND HYDROGEN. 